Field of the Invention
The present invention relates to an oxide sintered body and a process for manufacturing the oxide sintered body composed of an oxide mainly comprising indium and silicon, and also, to an oxide film obtained by using the oxide sintered body. In addition, the present application claims priority based on the Japanese Patent Application No. 2014-113139 filed on May 30, 2014 in Japan.
Description of Related Art
The oxide film has been used in various ways such as electrode of various light reception elements, i.e. solar battery, liquid crystal display element, and else, or various antifogging transparent heating elements, i.e. heat-ray reflective film for cars or construction, antistatic film, freezing show case, and else. Also, it is applied as optical film represented by antireflective film, reflection increasing film, interference film, polarizing film, and else. As the optical film, it is applied as a laminated body combining the oxide films having various features.
A spectral characteristic of oxide multi-layered film is decided by film thickness “d” and refractive index “n” of each layer, when extinction coefficient k can be regarded as almost zero. Therefore, in optical design of the laminated body using oxide film, it is generally carried out by a calculation based on data of “d” and “n” of each layer configuring the oxide multi-layered film. In this case, in addition to combining high refractive index film and low refractive index film, also by adding a film having intermediate refractive index of these films (intermediate refractive index film), a multi-layered film having superior optical characteristic can be obtained.
As general high refractive index film (n>1.90), TiO2 (n=2.4), CeO2 (n=2.3), ZrO2 (n=2.2), Nb2O5 (n=2.1), Ta2O5 (n=2.1), WO3 (n=2.0) and else are known. As low refractive index film (n<1.60), SiO2 (n=1.4), MgF2 (n=1.4) and else are known. As intermediate refractive index film (n=1.60 to 1.90), Al2O3 (n=1.6), MgO (n=1.7), Y2O3 (n=1.8) and else are known.
As a process for forming these oxide films, sputtering process, vapor deposition process, ion plating process, solution coating process and else are generally known. Among those, the sputtering process is widely used in industry, as the operation is very easy, and as it is useful when film formation of material with low vapor pressure or precise control of film thickness is required.
In concrete sputtering process, a target is used as raw material of various oxide films. This process generates argon plasma by causing glow discharge between an anode and a cathode, generally under gas pressure of about 10 Pa or less, with substrate as the anode and with target as the cathode. And it forms a film by colliding argon positive ion in the plasma to the target of the cathode, and by depositing particles of target component ejected by the collision on the substrate.
The sputtering process is classified by the generation process of argon plasma, and the process using radio frequency plasma is called radio frequency sputtering process and the process using direct current plasma is called direct current sputtering process. Generally, the direct current sputtering process is used widely in the industry for the reasons such that a deposition rate is faster compared to the radio frequency sputtering process, and that power source facility is inexpensive, and that an operation of film formation is easy. For example, in manufacturing of transparent conductive thin film, direct current magnetron sputtering process is widely adopted.
However, generally, in the sputtering process, when a raw material of the target is insulating target, it is necessary to use radio frequency sputtering process, and it will be impossible to obtain high deposition rate with this process.
On the other hand, the general intermediate refractive index materials, such as the above Al2O3, MgO, Y2O3 and else, are all poor in conductivity, and it is not possible to achieve the stable discharge when used for sputtering target as it is. Therefore, it is necessary to perform sputtering (reactive sputtering process) while reacting metal particles and oxygen in an atmosphere including a lot of oxygen by using metal target having conductivity, in order to obtain the intermediate refractive index film by the sputtering process.
However, in the reactive sputtering process including a lot of oxygen, its deposition rate is extremely slow, so the productivity will be impaired significantly. As a result, there are industrial problems such that a unit cost of the obtained intermediate refractive index film will be expensive, and else.
Here, as a material for obtaining the intermediate refractive index film, In—Si—O based oxide sintered body is proposed (For example, refer to D1.). Normally, In—Si—O based oxide sintered body comprising high concentration Si is poor in sinterability. From this point, in the technology described in D1, a sintered body is obtained from indium oxide powder and Si powder as raw materials, and also, by using hot press process, in order to solve these problems.
Patent Document 1: JP 4915065 B
Patent Document 2: JP 4424889 B
Patent Document 3: JP 2007-176706 A
Patent Document 4: JP 4028269 B